Biomedical subjects

C Y Kwan

Publications and source records attributed to C Y Kwan.

At least 91 records · Page 5Linked to original sources

PubMed1995

Alterations in beta-adrenoceptors and polyploidy in cultured aortic smooth muscle cells from different age groups of spontaneously hypertensive rats and Wistar-Kyoto rats.

OBJECTIVE: The relationship between the number of beta-adrenoceptors and polyploidy in cultured aortic smooth muscle cells derived from different age groups of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were examined. DESIGN: The number of beta-adrenoceptors, the percentage of multinucleated cells and the incidence of polyploidy from cultured smooth muscle cells derived from SHR and WKY rats aged 3-4, 10-12 and 28-30 weeks were measured. The effect of passaging of the cells on the expression of beta-adrenoceptors and polyploidy on cultured smooth muscle cells from both SHR and WKY rats was also investigated. METHODS: Receptor binding experiments were carried out using [125]-monoiodocyanopindolol with osmotically lysed cultured aortic smooth muscle cells to investigate the properties of vascular beta-adrenoceptors in SHR and WKY rats. The proportion of polyploid smooth muscle cells was determined by frequency distribution analyses of Feulgen DNA microdensitometric measurements. RESULTS: The incidence of polyploid smooth muscle cells was consistently higher in cells cultured from SHR than in those from WKY rats in all three age groups, with a positive correlation between polyploidy and age in SHR. Furthermore, in all three age groups the number of beta-adrenoceptor binding sites was also higher in cultured smooth muscle cells from SHR than in those from WKY rats. There was no significant difference in the receptor affinity. The increase in beta-adrenoceptor number was associated with an increase in polyploidy, and both of these changes were positively correlated both with the age of the rats from which these cells were derived and with the number of passages. CONCLUSIONS: Under cell culture conditions the expression of beta-adrenoceptor density increases with the number of passages in both SHR and WKY rats. Smooth muscle cells derived from older SHR and WKY rats have a greater propensity to develop polyploidy. This trend is significantly accelerated in cultured smooth muscle cells derived from SHR compared with those from WKY rats, suggesting a premature ageing process. These findings suggest that, in cultured smooth muscle cells from SHR and WKY rats, beta-adrenoceptors may influence the expression of polyploidy.

Animals↗

PubMed1995

Activation of protein kinase C as a modulator of potentiated UK-14304-induced contractions in dog mesenteric artery and vein.

We assessed the role of protein kinase C (PKC) in the mechanism responsible for the potentiation of UK-14304-induced contractions produced when isolated dog mesenteric vascular rings were pretreated with threshold concentrations of 12-O-tetradecanoyl-phorbol-13-acetate (TPA), KCl, or endothelin-1 (ET-1). In dog mesenteric artery. UK-14304 produced a biphasic concentration-response curve in the presence of TPA, KCl, or ET-1, with the curve portion at lower concentrations being alpha 2-adrenoceptor dependent and the portion at higher concentrations being alpha 1-adrenoceptor dependent. Calphostin C (10(-6)M), a PKC inhibitor, abolished amplified UK-14304-induced contraction in the TPA-pretreated tissues. In the KCl- and ET-1-pretreated tissues. 10(-6)M calphostin C antagonized amplified UK-14304-induced contractions by approximately 20% in both parts of the concentration-response curve. In contrast, in dog mesenteric vein, amplified UK-14304-induced contractions by TPA, KCl, and ET-1 were entirely dependent on alpha 2-adrenoceptors. Calphostin C (10(-6)M), which in control experiments had no effect on KCl-induced contraction and antagonized responses to TPA by 60.1%, inhibited UK-14304-induced contraction by 18.3%. Amplified UK-14304-induced contraction was antagonized by 10(-6)M calphostin C by 21.8% in KCl-precontracted tissues, 58.1% in ET-1-precontracted tissues, and 66.3% in TPA-precontracted tissues. In the ET-1- and TPA-pretreated dog mesenteric veins, 10(-6)M calphostin C decreased maximal tensions of enhanced UK-14304-induced contractions to the same level as the UK-14304-induced maximal tension inhibited by 10(-6)M calphostin C in untreated dog mesenteric vein. Therefore, TPA can be a precontracting agent that amplifies UK-14304-induced contractions through PKC activation in both dog mesenteric artery and vein. PKC predominantly mediates the contraction amplification mechanisms after exposure to ET-1 in dog mesenteric vein and does not play a major role in the amplification of UK-14304-induced contraction by KCl in both dog mesenteric artery and vein. These data show that a common mechanism need not underlie amplification of adrenergic responses in mesenteric artery and vein.

Adrenergic alpha-Agonists↗

PubMed1995

Regulation of vascular contraction by ionic matrix surfaces of the smooth muscle cell: changes in SHR?

1. KCl-induced contractions in aortic rings of spontaneously hypertensive rats (SHR) and two normotensive strains, Sprague-Dawley (SD) and Wistar-Kyoto (WKY) rats, were studied. 2. The contraction elicited by isotonic Na-free, KCl solution containing 2.5 mmol/L Ca and 1 mmol/L Mg was concentration-dependently inhibited by Na and K. Maximal inhibition was induced by 20 mmol/L NaCl in WKY and SHR (65 and 85%, respectively) and by 60 mmol/L NaCl in SD (50%). KCl (10-40 mmol/L) had no effect on SD but produced almost full relaxation in WKY and about 50% relaxation in SHR. 3. Isotonic Ca-free, Na-free high Mg (2 mmol/L), K-solution caused strong phasic contractions in WKY and SHR, but weak responses in SD. 4. Aortic rings of SD, WKY and SHR developed strong, sustained and reproducible contractions in isotonic Ca-free, Na-free, K-solution containing EDTA, which were fully relaxed by 1.2, 1.6 and 8 mmol/L Na, respectively. 5. We suggest that the primary mechanism of KCl-contraction is potential-independent competition between monovalent and divalent cations for binding sites on both surfaces of the plasma membrane (e.g. K with Mg and Na with Ca) and that differences in aortic contractility in SHR, WKY and SD merely reflect strain differences in the composition of the ionic matrix, independent of hypertension.

Animals↗

PubMed1995

Vascular effects of selected antihypertensive drugs derived from traditional medicinal herbs.

1. The pharmacological actions of the active ingredients extracted or purified from two selected traditional Chinese medicinal plants on vascular smooth muscles are briefly reviewed. The active ingredients of these herbal drugs include tetrandrine (TET) and total ginseng saponins (TGS). These natural products have been clinically used in China for the treatment of cardiovascular diseases due to their vasodilatory and antihypertensive actions. 2. Studies from this laboratory have confirmed previously reported characteristics of these drugs as Ca2+ antagonists in vascular tissues. On the other hand, they also elicited inhibitory effects in response to a wide variety of receptor stimulations as indicated by contractility studies using isolated vascular tissues and radioligand binding studies using isolated subcellular membranes. 3. TET has been demonstrated as an effective but not very selective Ca2+ antagonist. Other than the vasodilatory action on arteries and veins, TET also shows a vasoconstrictive effect in veins. 4. TGS from panax notoginseng may be acting as a novel and selective Ca2+ antagonist that does not interact with the L-type Ca2+ channel (e.g. in KCl-induced contraction) but may interact with the putative receptor operated Ca2+ channel (e.g. in phenylephrine-induced contraction). TGS from panax quinquefolium, on the other hand, enhanced the vasoconstrictor effect produced by phenylephrine, but not KCl.

Alkaloids↗

PubMed1995

Regulation of vascular tone: cross-talk between sarcoplasmic reticulum and plasmalemma.

Selected topics on the roles of sarcoplasmic reticulum (SR) in the control of vascular smooth muscle (VSM) tone are briefly reviewed with particular reference to the regulation of cytosolic concentration of free calcium ions, [Ca2+]i. Although morphological evidence and subcellular membrane studies indicate a relatively meager quantity of SR in VSM and of endoplasmic reticulum (ER) in endothelial cells (ECs) compared with skeletal muscle and cardiac muscle, contractility studies suggest that vascular tone is, to a large extent, regulated by the intracellular Ca2+ stores in smooth muscle and endothelial cells. Cytosolic Ca2+ levels control myosin light chain phosphorylation and contraction in VSM and activation of NO synthase and phospholipase A2 in ECs to regulate nitric oxide (NO) and prostaglandin I2 formation. Understanding of the importance of SR or ER in modulating the [Ca2+]i in VSM and ECs has been further advanced as a result of the new development and refinement of biophysical techniques in the measurement of cellular Ca2+ concentrations and ion currents, such as fluorescent Ca2+ indicators and patch-clamp techniques. Experimental evidence has accumulated in support of the existence of cross-talk between SR-ER and the plasma membrane (PM). Novel pharmacological tool drugs selective for the SR-ER Ca2+ pump, such as thapsigargin and cyclopiazonic acid, as well as for SR-ER Ca2+ channels, such as ryanodine (for the Ca(2+)-induced Ca2+ release channel) and inositol polyphosphates and heparin (for the inositol-1,4,5-trisphosphate activated Ca2+ channel), together with the use of blockers for selective PM Ca2+ channels have enabled better formulation and elucidation of the mechanisms of cross-talk between SR-ER and PM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Characterization of alpha 2 adrenoceptors and other adrenoceptors in membranes isolated from dog mesenteric nerve axons.

The axonal membranes from dog mesenteric nerves were isolated and characterized. They had a high density of [3H]saxitoxin, [3H]rauwolscine and [125I]iodocyanopindolol binding sites, but low densities of [125I] omega-conotoxin (GVIA) and [3H]prazosin binding sites. The microsomal membranes had one of the higher densities of [3H]rauwolscine binding sites in centrifugation fractions. These sites were characterized by saturation, kinetic and competition studies. In competition with oxymetazoline, WB 4101, prazosin, ARC-239, SK&F 104078 and SK&F 104856, these rauwolscine binding sites were alpha 2A-like. Chloroethylclonidine pretreatment did not affect the ability of SK&F 104078 or SK&F 104856 to compete with rauwolscine binding sites on axonal membranes. Bmax values were unchanged by chloroethylclonidine under conditions that also failed to reduce Bmax values of rauwolscine binding to membranes from human platelets. These receptors appear to be alpha 2A adrenoceptors and may represent sites of prejunctional control of neurotransmitter release in the dog. This membrane preparation may be useful in biochemical studies of prejunctional neural receptors.

Adrenergic alpha-Agonists↗

PubMed1995

Calcium antagonistic actions of tetrandrine depend on cell types.

We examined the effects of tetrandrine (TET) on Ca2+ mobilization in various types of cells using inositol trisphosphate-generating drugs and compared it with those using the microsomal Ca(2+)-ATPase inhibitor thapsigargin (TG) which is a tool for analyzing Ca2+ store-regulated Ca2+ entry (capacitative Ca2+ entry). In rat pheochromocytoma PC12 cells, 100 microM TET abolished high K+ (30 mM)-induced sustained increase in [Ca2+]i and partially inhibited bradykinin (1 microM)-induced or TG (100 nM)-induced Ca2+ entry. In NIH/3T3 fibroblasts, 100 microM TET abolished Ca2+ entry induced by bombesin (1 microM) or TG (100 nM). In rat glioma C6 cells, the addition of 100 microM TET reduced the sustained elevation of [Ca2+]i induced by endothelin 1 (10 nM) or TG (100 nM) declining to the resting level. In rat parotid acinar cells, 100 microM TET abolished a sustained increase in [Ca2+]i induced by carbachol (100 microM) or TG (100 nM). In human leukemia T-cell line Jurkat, 100 microM TET did not inhibit Ca2+ entry evoked by the anti-CD3 antibody OKT3 (10 micrograms/ml) or TG (100 nM). The present results suggest that the action of TET on Ca2+ entry is dependent on cell types.

Alkaloids↗

PubMed1995

beta-Adrenoceptor activates endothelium-dependent release of nitric oxide in rat aorta.

AIM: To examine the possible role of agents elevating cAMP to release NO from aortic endothelial cells. METHODS: NG-nitro-L-arg inine methylester (L-NAME), an inhibitor of NO synthase, partially inhibited endothelium-dependent relaxation evoked in phenylephrine-precontracted rings by isoproterenol and abolished relaxation mediated by forskolin 0.2 mumol L-1. RESULTS: In rings without endothelium, isoproterenol and forskolin were less effective relaxants and L-NAME had no effect on the responses. In methylene blue-treated rings isoproterenol- and forskolin-induced relaxation were prevented in both endothelium-intact and -denuded rings, but the inhibitory effect of methylene blue were significantly more in rings with endothelium than in those without. On the other hand, relaxation induced by sodium nitroprusside was not inhibited by L-NAME, but was inhibited by methylene blue in both the endothelium-intact and -denuded rings. The concentration-relaxation curves to sodium nitroprusside after methylene blue were identical for rings with and without endothelium. CONCLUSION: beta-Adrenoceptors or any agent which raises cAMP elevate NO release from endothelial cells.

Adrenergic beta-Agonists↗

PubMed1994

Cytosolic calcium pre-elevation amplifies agonist-induced calcium release in human leukaemic HL-60 cells.

Histamine, ATP, and two microsomal Ca(2+)-pump inhibitors, thapsigargin (TG) and cyclopiazonic acid (CPA), were able to release intracellular Ca2+ in human leukaemic HL-60 cells. The relationships between the agonist-, TG- and CPA-sensitive Ca2+ pools were investigated with optimal concentrations of these agents in Ca(2+)-free medium. CPA failed to release Ca2+ after the Ca2+ stores of the cells had been discharged by TG, and vice versa, suggesting that the TG- and CPA-sensitive pools exactly overlap. Using this protocol, it was further demonstrated that (a) histamine and ATP utilized the same agonist-sensitive pool, and (b) the CPA- or TG-sensitive pool was much larger than, and encompassed, the agonist-sensitive pool. Although optimal (30 microM) CPA treatment for 5 min totally emptied the agonist-sensitive pool, a brief exposure (1.5 min) to a sub-optimal concentration (3 microM) of CPA, which only slightly raised cytosolic free Ca2+ concentration ([Ca2+]i), substantially enhanced subsequent agonist-induced Ca2+ release. Brief pretreatments with sub-optimal concentrations of TG or ionomycin, which caused moderate [Ca2+]i elevation, also caused such enhancement. However, sub-optimal CPA pretreatment had no prominent effect on Ca2+ release, which was InsP3-independent: it did not enhance TG-induced Ca2+ release, and only relatively weakly augmented ionomycin-induced Ca2+ release. Our results represent a novel observation showing that low concentrations of CPA, TG and ionomycin can potentiate subsequent agonist-induced Ca2+ release, and suggest that a 'priming' moderate [Ca2+]i elevation can amplify subsequent InsP3-dependent Ca2+ release in HL-60 cells.

Adenosine Triphosphate↗

PubMed1994

Analogues of tetramethylpyrazine affect membrane fluidity of liposomes: relationship to their biological activities.

Several structurally similar pyrazine derivatives, tetramethylpyrazine, triethylpyrazine and tetraethylpyrazine have previously been found to inhibit a broad spectrum of plasmalemma-associated biological activities of various tissues, including ion channels and membrane receptors in a given order of potency that increases with increasing bulkiness and hydrophobicity of these drugs. Our earlier speculation that the multiple membrane effects elicited by these pyrazine derivatives were associated with changes in the bulk physical properties of the biological membranes in the presence of these drugs was confirmed by fluorescence polarization and electron spin resonance studies. Since biological membranes contain a complicated mixture of a large variety of lipids and proteins, we chose to study the molecular properties of the interaction of these three pyrazine derivatives using a simple model system composed of synthetic phospholipids. We measured the effects of the drugs on the fluidity (or microviscosity) of these model membranes, as well as determining the phase-transition properties of the model membranes with the use of fluorescence polarization, electron spin resonance and differential scanning calorimetry. All the methods employed yielded qualitatively similar results. Tetramethylpyrazine, the smallest and the least hydrophobic amongst these three drugs, had minimal or no effect on the phase-transition of phospholipids based on temperature dependence studies, whereas tetraethylpyrazine, the largest and the most hydrophobic of the three, elicited the most potent effect in a concentration-dependent manner. These results could be attributed to the amount of incorporation of these pyrazine derivative into the liposomes, an interaction which occurs more favourably at temperatures above the gel to liquid crystalline phase-transition temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry, Differential Scanning↗

PubMed1994

Plant-derived drugs acting on cellular Ca2+ mobilization in vascular smooth muscle: tetramethylpyrazine and tetrandrine.

The pharmacological profiles of the active ingredients extracted and purified from two well-known Chinese traditional medicinal plants were reviewed. These herbal drugs include tetramethylpyrazine (TMP) and tetrandrine (TET); both have been clinically used in China for the treatment of cardiovascular diseases due to their vasodilatory actions. Studies from this laboratory have confirmed previously reported characteristics of TMP as a Ca2+ antagonist in vascular tissues. However, it also elicited inhibitory effects in response to a wide variety of receptor stimulations as indicated by functional studies and radioligand binding studies using isolated subcellular membranes. TET also inhibited the vascular contraction in response to depolarization by KCl and phenylephrine. It has been found to interact directly with the L-type Ca2+ channel and alpha-adrenoceptor subtypes. Recently, its action on T-type Ca2+ channels has also been demonstrated. These findings collectively suggest that studies of the vasodilatory and antihypertensive effects of these plant-derived drugs on the regulation of cytosolic Ca2+ in vascular smooth muscle are consistent with the current hypothesis of Ca2+ dysfunction as an important etiological factor for the pathogenesis of hypertension.

Alkaloids↗

PubMed1994

Sensitivity to protein kinase C inhibitors of nicardipine-insensitive component of high K+ contracture in rat and guinea-pig aorta.

1. In the rat and guinea-pig aorta, we observed that the contraction to hypertonically-added K+, unlike the isotonic K(+)-induced contraction, was only partially sensitive to nicardipine (0.1, 1 and 10 microM), an L-type Ca2+ channel blocker and occurred in Ca(2+)-free medium containing 50 microM EGTA. We have characterized this nicardipine-insensitive hypertonically-added K+ contraction. 2. The contraction induced by an equi-osmolar concentration of mannitol was similar in size to that evoked by hypertonically-added K+. 3. When the tissue was depleted of its internal Ca2+ stores with various agents such as phenylephrine (10 microM) cyclopiazonic acid (30 microM), thapsigargin (1 microM) or ryanodine (30 microM), or by incubation in Ca(2+)-free medium over 30 min, little effect was observed on the high K+ contracture in the presence of L-type Ca2+ channel blockade. 4. Phentolamine (10 microM) or indomethacin (10 microM) did not reduce the contraction induced by high K+. 5. Application of a protein kinase C inhibitor, H7 (10, 30 and 100 microM) or calphostin C (1 microM), reduced the high K+ contraction but not that caused by an equi-osmolar concentration of mannitol. 6. The data suggest that hypertonic K(+)-induced contraction differs from that caused by hypertonicity or depolarization per se and invokes membrane enzyme activation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1994

Dual effects of tetrandrine on cytosolic calcium in human leukaemic HL-60 cells: intracellular calcium release and calcium entry blockade.

1. Tetrandrine (TET, a Ca2+ antagonist of Chinese herbal origin) and thapsigargin (TSG, an endoplasmic reticulum Ca2+ pump inhibitor) concentration-dependently mobilized Ca2+ from intracellular stores of HL-60 cells, with EC50 values of 20 microM and 0.8 nM, respectively. After intracellular Ca2+ release by 30 nM TSG, there was no more discharge of Ca2+ by TET (100 microM), and vice versa. 2. Pretreatments with 100 nM rauwolscine (alpha 2-adrenoceptor antagonist), 100 nM prazosin (alpha 1-adrenoceptor antagonist), 10 nM phorbol myristate acetate (PMA, a protein kinase C activator) or 100 nM staurosporine (a protein kinase C inhibitor) had no effect on 100 microM TET-induced intracellular Ca2+ release. 3. After intracellular Ca2+ release by 30 nM TSG in Ca(2+)-free medium, readmission of Ca2+ caused a substantial and sustained extracellular Ca2+ entry. The latter was almost completely inhibited by 100 microM TET (IC50 of 20 microM) added just before Ca2+ readmission. In Ca(2+)-containing medium, 30 nM TSG caused a sustained phase of cytosolic Ca2+ elevation, which could be abolished by 100 microM TET. TET was also demonstrated to retard basal entry of extracellular Mn2+ and completely inhibit TSG-stimulated extracellular Mn2+ entry. 4. TSG-induced extracellular Ca2+ entry was insensitive to the L-type Ca2+ channel blocker, nifedipine (1 microM), but was completely inhibited by the non-selective Ca2+ channel blocker La3+ (300 microM). Depolarization with 100 mM KCl did not raise the cytosolic Ca2+ level. 5. These data suggest that (a) TET and TSG mobilized the same Ca2+ pool and TET-induced intracellular Ca2+ release was independent of protein kinase C activity and ox-adrenoceptor activation,and (b) TET blocked the voltage-insensitive Ca2+ entry pathway activated by TSG. These dual effects on HL-60 cells were also observed with hernandezine (HER), a TET-like compound and in another cell type, murine B lymphoma M12.4 cells.

Alkaloids↗

PubMed1994

Investigation of alpha 1-adrenoceptor subtypes in canine aorta, using alkylating agents.

The ability of putative selective irreversible ligands SZL-49 (1-(4-amino-6,7-dimethoxy-2,5-diene-2-carbonyl)) and CEC (chlorethylclonidine), for alpha 1A and alpha 1B adrenoceptor subtypes, respectively, to affect alpha 1-adrenoceptors of canine aorta microsomal membranes was investigated. These membranes contain an apparently homogeneous population of [3H]prazosin binding sites. SZL-49, like phenoxybenzamine, abolished all binding of [3H]prazosin. CEC abolished 75% of the prazosin binding sites under the most stringent conditions we applied. However, the remaining 25% of binding sites was identical in affinity for prazosin with control membranes, and competition studies of other subtype-selective ligands revealed unchanged ability to complete against CEC-sensitive and -insensitive sites. We concluded that SZL-49 and CEC are not alpha 1A- and alpha 1B-adrenoceptor selective under in vitro conditions. Our data led to the hypothesis that canine aortic membranes contain exclusively alpha 1B-adrenoceptors but that current tools for identifying alpha 1-adrenoceptor subtypes proved inadequate in vitro in this study.

Adrenergic alpha-1 Receptor Antagonists↗

PubMed1994

Effects of sarcoplasmic reticulum calcium pump inhibitors on vascular smooth muscle.

A dysfunctioning of Ca2+ pump ATPase in the sarcoplasmic reticulum in vascular smooth muscle has been proposed as a contributing factor for the development of genetic hypertension. In this study, we determined whether in vitro inhibition of the sarcoplasmic reticulum Ca2+ pump in vascular smooth muscle tissues and cultured cells isolated from aortas of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats would elicit the known alterations of contractile function and cell growth. We found the following common vascular effects of thapsigargin and cyclopiazonic acid, which are known to be selective inhibitors of sarcoplasmic reticulum Ca(2+)-ATPase in a number of tissues including smooth muscle: (1) Both sarcoplasmic reticulum Ca2+ pump inhibitors diminished agonist-induced transient contraction in Ca(2+)-free medium (ie, contraction due to intracellular release of Ca2+) and enhanced nifedipine-sensitive contraction on readmission of Ca2+ (ie, Ca2+ influx via L-type channels); and (2) thapsigargin and cyclopiazonic acid inhibited the attachment of cultured aortic muscle cells to the substrate in a similar degree in both SHR and WKY cells, but SHR cells were more sensitive than WKY cells to the inhibition of cell proliferation by these two agents. The first effect may provide an explanation for several contractile abnormalities known to be associated with elevated cytosolic Ca2+ concentration, whereas the second effect suggests that elevation of cytosolic Ca2+ in aortic smooth muscle cells is not necessarily associated with or sufficient to account for the accelerated cellular proliferation in SHR. These results, however, further stress the functional importance of impairment of Ca2+ regulation in vascular smooth muscle cells in genetic hypertension.

Animals↗

PubMed1994

Effects of Panax notoginseng saponins on receptor-operated Ca2+ channels in vascular smooth muscle.

The effects of saponins of Panax notoginseng (PNGS) on the alpha-adrenoceptor agonists-induced contractile responses and Ca2+ movement were studied in dog mesenteric artery (MA) and saphenous vein (SV). PNGS reduced the contractions and the 45Ca influx (from 0.36 +/- 0.03 to 0.14 +/- 0.05 mumol.g-1 wet strip) induced by phenylephrine (Phe) without effect on KCl-induced contraction and 45Ca influx which were nearly completely inhibited by nifedipine 0.1 mumol.L-1. PNGS did not change the 45Ca efflux induced by Phe and the Kd value (from 0.76 +/- 0.04 to 0.72 +/- 0.15 nmol.L-1) for [3H]prazosin binding on the microsomal membrane isolated from MA. Our results indicate that PNGS selectively inhibits Ca2+ entry through receptor-operated Ca2+ channel.

Adrenergic alpha-Agonists↗

PubMed1994

Amplification of 5-hydroxytryptamine-induced contractile responses via 5-hydroxytryptamine receptors and alpha-adrenoceptors in dog mesenteric artery and vein.

The interactions between 5-hydroxytryptamine (5-HT) and both serotonergic and alpha adrenoceptors were investigated by using isolated dog mesenteric vascular rings mounted in tissue baths for the measurement of isometric contraction. In the mesenteric artery, 5-HT elicited concentration-dependent contractions, producing 46.5% of the KCl maximal response. At low concentrations, the 5-HT-induced contraction was effectively inhibited by 10(-6) M methysergide and by 10(-6) M ketanserin, but was prazosin-resistant. At high 5-HT concentrations, the contractile response was effectively antagonized by 10(-7) M prazosin. The presence in the medium of 20 mM KCl, which increased resting tension less than 10% of the KCl maximal response, markedly enhanced the responses to 5-HT primarily at concentrations lower than 10(-5) M. These amplified responses were methysergide-sensitive, but prazosin- and ketanserin-resistant. In the mesenteric vein, exposure to 5-HT caused an extremely small contraction, producing 5.2 +/- 4.3% of the KCl maximal response. In the presence of 20 mM KCl, which had small contractile effects, 5-HT produced a biphasic concentration-response curve. Methysergide (10(-6) M) and 10(-6) M ketanserin effectively inhibited the responses to low concentrations of 5-HT, and only 10(-7) M rauwolscine effectively blocked the responses to high concentrations of 5-HT. In the dog mesenteric artery, our data suggest that addition of threshold concentrations of KCl enhanced the contractile response to 5-HT through amplification of 5-HT1-like receptor-mediated responses. In the dog mesenteric vein, KCl enhanced 5-HT responses via amplification of both 5-HT2 receptor- and alpha-2 adrenoceptor-mediated responses.

Animals↗

PubMed1993

Characterization of [3H]ryanodine binding sites in smooth muscle of dog mesentery artery.

The ryanodine receptor has been widely demonstrated to be a Ca2+ release channel in both skeletal and cardiac muscle. Ryanodine also functionally affects Ca2+ release from an intracellular pool of smooth muscle. In the present study, both high and low affinity ryanodine binding sites are identified in dog mesenteric artery (with Kd 5 nM and 269 nM, respectively). [3H]ryanodine binding is not correlated with the density of innervation in different smooth muscles. This study provides direct evidence of the presence of ryanodine binding sites in dog mesentery artery. These ryanodine binding sites are of smooth muscle origin.

Animals↗